ELECTROHYDRODYNAMIC INSTABILITY OF LIQUID SHEET SATURATING POROUS MEDIUM WITH INTERFACIAL SURFACE CHARGES

2013 ◽  
Vol 23 (2) ◽  
pp. 165-191
Author(s):  
Mohamed F. El-Sayed ◽  
M. H. M. Moussa ◽  
Ahmed A. A. Hassan ◽  
N. M. Hafez
Keyword(s):  
Porous Medium ◽  
Liquid Sheet ◽  
Surface Charges ◽  
Electrohydrodynamic Instability ◽  
Interfacial Surface

Nonlinear Electrohydrodynamic Stability of Two Superposed Bounded Fluids in the Presence of Interfacial Surface Charges

1998 ◽  
Vol 53 (5) ◽  
pp. 217-232 ◽  
Author(s):  
M. F. El-Sayed ◽  
D. K. Callebaut
Keyword(s):  
Schrödinger Equation ◽  
Electric Field ◽  
Nonlinear Schrödinger Equation ◽  
Schrodinger Equation ◽  
Nonlinear Schrodinger Equation ◽  
Surface Charges ◽  
Nonlinear Schrödinger ◽  
Interfacial Surface ◽  
Lower Fluid ◽  
The One

Abstract The method of multiple scales is used to analyse the nonlinear propagation of waves on the interface between two superposed dielectric fluids with uniform depths in the presence of a normal electric field, taking into account the interfacial surface charges. The evolution of the amplitude for travelling waves is governed by a nonlinear Schrödinger equation which gives the criterion for modulational instability. Numerical results are given in graphical form, and some limiting cases are recovered. Three cases, in the pure hydrodynamical case, depending on whether the depth of the lower fluid is equal to or greater than or smaller than the one of the upper fluid are considered, and the effect of the electric field on the stability regions is determined. It is found that the effect of the electric field is the same in all the cases for small values of the field, and there is a value of the electric field after which the effect differs from case to case. It is also found that the effect of the electric field is stronger in the case where the depth of the lower fluid is larger than the one of the upper fluid. On the other hand, the evolution of the am-plitude for standing waves near the cut-off wavenumber is governed by another type of nonlinear Schrödinger equation with the roles of time and space are interchanged. This equation makes it possible to determine the nonlinear dispersion relation, and the nonlinear effect on the cut-off wavenumber.

scholarly journals High Electromechanical Deformation Based on Structural Beta-Phase Content and Electrostrictive Properties of Electrospun Poly(vinylidene fluoride- hexafluoropropylene) Nanofibers

Polymers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1817 ◽  
Author(s):  
Nikruesong Tohluebaji ◽  
Chatchai Putson ◽  
Nantakan Muensit
Keyword(s):  
Dielectric Properties ◽  
Smart Materials ◽  
Microelectromechanical Systems ◽  
Vinylidene Fluoride ◽  
Interfacial Polarization ◽  
Surface Charges ◽  
Thermal Compression ◽  
Β Phase ◽  
Interfacial Surface ◽  
Poly Vinylidene Fluoride

The poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) polymer based on electrostrictive polymers is essential in smart materials applications such as actuators, transducers, microelectromechanical systems, storage memory devices, energy harvesting, and biomedical sensors. The key factors for increasing the capability of electrostrictive materials are stronger dielectric properties and an increased electroactive β-phase and crystallinity of the material. In this work, the dielectric properties and microstructural β-phase in the P(VDF-HFP) polymer were improved by electrospinning conditions and thermal compression. The P(VDF-HFP) fibers from the single-step electrospinning process had a self-induced orientation and electrical poling which increased both the electroactive β-crystal phase and the spontaneous dipolar orientation simultaneously. Moreover, the P(VDF-HFP) fibers from the combined electrospinning and thermal compression achieved significantly enhanced dielectric properties and microstructural β-phase. Thermal compression clearly induced interfacial polarization by the accumulation of interfacial surface charges among two β-phase regions in the P(VDF-HFP) fibers. The grain boundaries of nanofibers frequently have high interfacial polarization, as they can trap charges migrating in an applied field. This work showed that the combination of electrospinning and thermal compression for electrostrictive P(VDF-HFP) polymers can potentially offer improved electrostriction behavior based on the dielectric permittivity and interfacial surface charge distributions for application in actuator devices, textile sensors, and nanogenerators.

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